Yellow Rattle – guest blog post by Nick Mann, Director of Habitat Aid

Yellow Rattle, Rhinanthus minor

Yellow Rattle, or Hay Rattle, or Cockscomb, used to be a common plant of short grassland. The rattle of its delicate disc like seeds was traditionally a harbinger of the harvest. It’s a pretty annual wildflower and is still found across the UK, including Highland Machair. We think there are at least 6 sub-species across the country, which makes its appearance variable. Rattle is a helpful plant for bumblebees and butterflies, although its slightly complicated flowers are tricky for honeybees. With more visual imagination than I’ve got you might see a cockscomb in them.

Rattle has an interesting feature which makes it invaluable. Like its distant relation Eyebright, Euphrasia, it is hemi-parasitic. That’s to say it photosynthesises but is also partly parasitic on the roots of a host. That host can be grass. It’s difficult to describe the effect it has, but grasses are dramatically enfeebled. Affected plants look perfectly healthy but are just much smaller, and the sward less luxuriant. Rattle populations could reduce hay yields by 50%.

This makes it a fabulous plant for meadow making and a deeply unpopular one for farmers. As an annual, however, and given the recent shift to multiple silage cuts, it has been easy to eradicate. It’s apparently very tasty for livestock, but you can see why there is now so little of it about.

This is – obviously – very helpful if you’re trying to establish a wildflower meadow. Not only does the Rattle knock back surrounding grasses, but when it dies off, relatively early in the summer, it leaves a helpful hole for a wildflower to fill. The biggest challenge for meadow makers on all but low fertility soils is to keep grass under the cosh, allowing wildflowers to develop. Why is that?  So far as I understand it, the more nutrients you add to soil, the bigger and faster grasses – even nice shy meadow grasses – will grow. Not so with wildflowers. This effect is exaggerated when you are dealing with more aggressive grasses like Cocksfoot (Dactylis glomerata) too. Very quickly you will be looking at just grass.

Rattle isn’t a universal panacea for this problem. In higher fertility soils it will struggle to get going, as it’s out-competed in its early stages by the surrounding grass. This is particularly true if they’re thugs like perennial rye grass, Lolium perenne, which is the staple of most lawn mixes. It will invariably see Yellow Rattle off. Nor is it apparent in all meadows; we have some lovely old sites around us here in Somerset without it. It won’t persist unless it’s managed properly.

Establishment & Management

Rattle seed is tricky. It doesn’t have long viability, so you need to check it’s from the current harvest. It’s awkward to process too, so buy it from a reputable source; germination rates can vary enormously. This all means it’s pretty expensive, but it only needs sowing between 0.5g and 1g if you’re overseeding existing grass.

Yellow Rattle is usually already included in meadow seed mixes if you’re starting from scratch, but if you’re sowing in spring you could add more the following autumn. Why? Rhinanthus needs vernalization; it needs a prolonged period of cold before it germinates.

As Rattle parasitizes grass, sow it with grass seed or into an existing sward; don’t try to establish it in a seed tray. You can buy it in plugs, grown with a host plant. If you’re using seed, it’s important that beforehand you chain harrow or scarify the existing sward to open it up, and cut or graze it very short. The books say you need to see at least 50% earth. The seed needs to be in contact with the earth and the seedlings a chance to get going.

Mix the seeds with an inert carrier like sand to bulk them out. 0.5g/square metre is a rate so low most gardeners think it’s a misprint! If you’re seeding a larger area, mark it out with canes into 5m or 10m squares. The seeds are delicate, so hand broadcast rather than using a machine. Coverage won’t be uniform, but a natural look is what you’re after anyway.

Once seeded, lightly roll or tread in the seed to ensure good contact with the soil. The seeds are windblown, so this is particularly important. Keep the area seeded lightly grazed or mown over the winter, but stop in March to avoid chopping the seedlings’ heads off!

If you’re using Rhinanthus as a first step to converting existing sward to a wildflower meadow area and all goes well, watch what happens in the first summer. You may be blessed with a display of wildflowers you hadn’t seen before. You might not! Some people at this stage decide to add more species, either by seed or plugs.

Your Rattle won’t persist if you let the surrounding grasses get long and rank. It’s very much a plant of short grassland. This means being disciplined about your hay cut and winter regime – i.e. light grazing, or cutting and removing arisings. If you are, your Rhinanthus should self-seed very happily and spread.

Nick Mann is the Director of Habitat Aid which is a small business in Somerset selling plants and seeds via their online shop.
They particularly focus on native species sourced from British nurseries, growers and harvesters. They give half of their profits from online retail sales to small science based UK conservation charities as well as to community planting and seeding schemes.We are very grateful to be a recipient of this generosity.